What can I expect driving my new QX60 in St. Paul, MN, in the winter? How do they handle on snow and ice? How is the visibility through all the windows? I have read some complaints about the Dueller HP 20" tires.
As someone formerly from northern Illinois, I would put snow tires on. I'm now down in St. Louis where that's not necessary, but if I was where there was a lot of snow on the roads, a lot of the time, I'd put on snow tires and forget about it.
I would recommend winter tires because you're not only looking for better traction when starting and turning, but also stopping. No amount of traction control and electronic aids makes up for winter tires when it comes to braking distance.
As for the drive mode selector, you can not lock 4wd on Infiniti's anymore. All it does when you put it into SNOW mode is to slow down the throttle response.
I've driven the QX60 on the stock 18" tires with good success in the snow. They were relatively new tires (less than 5K miles). Personally, I'd do the same thing I've done with my Q50. Get a set of wheels that will fit the car, mount some good snow tires to them and use that set up in the winter.
As for winter tire brands, people who have them, swear by Nokians. But they're really expensive. I've had good experience with all brands of winter tires I've tried - at least for the first 2-3 seasons. Currently I'm running Blizzaks on my Q50. But really, any snow tire is going to be markedly better than any "all season" tire in the cold/wet/snow. Just take them off when the weather warms up so you don't wear them out prematurely.